Duplex radio system



A Nov; 5, 1946..

J. EVANS DUPLEX RADIO SYSTEM Filed Oct. 5, 1941 RECE/ VE HLA/MEM' auPPLYT3 ZZ Tf Z1 i PL/I'I'L' VOL TAGE m mmf/m 3a uw 7 Patented Nov. 5, 1946Fries rsi" DUPLEX RIO SYSTEM .lohn Evans, Palmyra, N. J., assigner toRadio Corporation of America, a corporation of Dela- Ware ApplicationGctober 3, 1941, Serial No. 413,423

(Cl. Z50- 9) '7 Claims. l

This invention relates to improvements in duplex'radio systems andparticularly to a system having a common antenna for transmitting pulsesignals and for receiving the pulse signals after reection.

Radio pulse echo systems, having a common antenna for transmitting andreceiving, have been described. Such systems generally depend upontransmission lines having critical lengths and critical impedances. Atthe instant of transmission the antenna represents a proper load for thetransmitter; at the same instant the transmission line to the receiverpresents a high impedance to the transmitter currents. After theradiation of the outgoing pulse, the line to the receiver becomes asuitable path for the received echo signals, and the transmission lineto the transmitter becomes a high impedance to the echo signals.

While such systems are entirely satisfactory for low and medium powervoperation, they become difficult to operate at higher powers. lFor eX-ample, for peak powers in excess of approximately kilowatts, the iirstthermionic tube of the receiver may not only overload but may beactually destroyed by the transmitted pulse which is applied through thehigh impedance path to the receiver. As the peak power increases, thedifculties of protecting the receiver increase with systems of thecharacter described.

It is an object of the instant invention to provide improved means foroperating a pulse echo system from a common antenna. Another object isto provide improved means for the duplex operation of a radio pulsetransmitter and radio pulse receiver on a common antenna. An additionalobject is to provide the receiver of a duplex pulse echo system with alimiter fed from a high impedance source.

The invention will be described by referring to the accompanyingdrawing, in which Figure l is a schematic diagram of a preferredembodiment of the invention; and Figure 2 is a graph illustrating theoperation of a limlter-rectiiier.

Referring to Fig. 1, a transmitter l is connected to an antenna 3, orother load circuit, by a transmission line 5. A receiver l' is alsoconnected to the antenna 3 by means of a second transmission Aline 9. Apair of limiter-rectiers il, i3 are interposed in the secondtransmission line between the antenna and the receiver. The rectiers.preferably of the thermionic type, are connected so that theirrespective cathodes are connected to their respective anodes to providea circuit which will transmit substantially equally both 2 positive andnegative half cycles of the applied high frequency current. The cathodesare energized through concentric lines l5, Il` The concentric lines areeach grounded at quarter wave lengths, or odd numbers of quarter wavelengths, of the carrier frequency currents of the pulses. The quarterwave lines present high impedances from the rectiers to ground, and thusminimize the vcurrents which ywould otherwise tend to flow to ground.

In the arrangement shown, the diameter of the second transmission linehas been increased to house the rectifers without crowding. In practice,since the rectiiiers arepreierably made very small to minimize theircapacity, they may be included within the line without increasing itscross-section. In the event that the cross-section of the line isincreased, any change in its characteristic impedance should be takeninto account in designing the system. Furthermore, the effect of therectier load on the transmitter line 5 and the antenna 3 should not beoverlookedl in matching the line to the load. f

The system operates as follows: .When the transmitter pulse is appliedto the line 5 and antenna 3, current-s will also now in the line 9 tothe receiver. The current to the receiver will be limited by the rectiercharacteristic which is illustrated in Fig. 2. It should be understoodthat the limiting characteristic of any one of the several curves 2l,23, etc., may be obtained'by adjusting the filament or cathodetemperature. Since the peak power of the outgoing pulses is many timesthat of the echo signal, the rectied current from the outgoing pulseswill be limited to a predetermined value, but the echo signals willoperate over the straight line portion 21 of the curve. The echo signalcurrents will therefore be transmitted without distortion and withnegligible attenuation to the receiver. It lshould be understood that inpulse echo operation the outgoing pulse is only transmitted for a brieftime during the operating cycle and the echoes are received during thebalance of the cycle, so that for all practical purposes the operationmay he described as duplex.

Thus the invention has been described as a.

duplex system in which a common antenna is used for transmitting pulsesof radio frequency energy and receiving the pulses lafter reflection.The effect of the high peak power of the transmitter on the receiver isminimized by inserting between the antenna and the receiver a full wavelimiter-rectifier. The rectiiier limits the ow of transmitter currentsto the receiver, and passes the echo currents to the receiver withoutdistortion and with negligible attenuation. While known rectiers ofother than the thermionic type may be used for thermionic rectiiers,means are provided for supplying the rectifier cathodes with energy overa path presenting a high impedance to the signaling currents.

I claim as my invention:

1. A duplexr radio system including in con bination a load circuit, atransmitter, a receiver having an input circuit, a transmission lineconnecting said load circuit to said transmitter, a second transmissionline connecting said load circuit to said receiver input circuit, and alimiterrectifier connected serially in one side of said transmissionline connecting said receiver input circuit and said load circuit tolimit the energy transferred from said transmitter through saidtransmission line to said receiver.

2. A duplex radio system including in combination an antenna, atransmitter, a receiver having an input circuit, a transmission lineconnecting said antenna to said transmitter, a second transmission lineconnecting said antenna to said receiver input circuit, and a full wavelimiter-rectier connected serially in one side of said transmission lineconnecting said receiver input circuit and said antenna to limit theenergy transferred from said transmitter through said transmission lineto said receiver. l

3. A duplex radio system including in combination a load circuit, aradio pulse transmitter, a radio. pulse receiver having an inputcircuit, a transmission line connecting said load circuit to saidtransmitter, a second transmission line connecting said. load circuit tosaid receiver input circuit, and a limiter-rectier connected serally inone side of said transmission line connecting said receiver inputcircuit and said load circuit to limit the pulse energy transferred fromthe transmitter through said transmission line to said receiver.

4. A duplex radio system including in combination an antenna, a radiopulse transmitter, a

radio pulse receiver having an input circuit, a transmission lineconnecting said antenna to said transmitter, a second transmission lineconnecting said antenna to said receiver input circuit, and a full wavelimiter-rectier connected serially in one side of said transmission lineconnecting said receiver input circuit and said antenna to limit thepulse energy transferred from the transmitter through said transmissionline to said receiver.

5. A duplex radio system including in combination a load circuit, aradio pulse transmitter, a radio pulse receiver, a transmission lineconnecting said transmitter to said load circuit, a second transmissionline connecting said receiver to said load circuit, a limiter-rectifierinterposed between said receiver and load circuit, and a pair of quarterwave transmission lines for supplying current to said rectifier over apath representing a high impedance to said pulses.

6. A duplex radio system including in combination an antenna, a radiopulse transmitter,-

a radio pulse receiver, a transmission line connecting said transmitterto said antenna, a second transmission line connecting said receiver tosaid antenna, a full wave limiter-rectier vinterposed between saidreceiver and antenna, and a pair of quarter wave transmission lines forsupplying current to said rectifier over a path representing a highimpedance to antenna currents.

'7. A duplex radio system including in lcombination an antenna, a radiopulse transmitter, a radio pulse receiver, a transmission lineconnecting said transmitter to said antenna, a seoond transmission lineconnecting said receiver to said antenna, a full wave limiter-rectifierinter-V posed between said receiver and antenna, a pair of transmissionlines for supplying current to said rectifier, and means grounding saidpair of lines at a length corresponding to an odd number of quarter wavelengths of the carrier frequency of said pulses so that a high impedanceis offered between said rectifier and ground.

JOHN EVANS-

